In the art of processing articles sensitive to contamination, such as glass plates for Liquid Crystal Displays (LCD's), solar panels, etc. (hereinafter referred to as "substrates"), it is desirable to have a process that has both an efficient cleaning capability and high throughput rate.
The present art includes primarily conveyorized processing and batch processing apparatuses. Conveyorized processing has the advantage of continuous processing and a potentially high throughput rate. Present systems convey the substrate with the substrate in horizontal and/or vertical orientations. The present art includes systems with brushes or other mechanical scrubbing devices which are used to remove undesired stains and particulates from the substrate surface. Because of the forces exerted by these scrubbing devices, grippers that contact an undesirable amount of substrate surface area are employed to hold and/or convey the substrate. This contact can leave microscopic particulates on the substrate surface, which are undesirable. Also, mechanical contact is employed to remove liquid from the surface of the substrate to reduce the amount of liquid carried on the substrate to previous or subsequent processes, a phenomenon known as "dragout." Dragout is undesirable from both the standpoint of cleaning efficiency and chemical waste treatment efficiency. In the cases where a gaseous barrier is used in place of mechanical contact, the consequence of drying the liquid prematurely on the substrate surface and depositing undesirable residues can result. Mechanical contact is also employed on the bottom surface of horizontally conveyed substrates to support the substrate from sagging or by a clamp or wheels or cylinders for vertically conveying substrates, both of which can leave unwanted microscopic debris on the substrate surfaces. As a result of these disadvantages, substrates processed with conveyorized equipment are typically only used for applications with relatively relaxed cleanliness requirements (such as glass for twisted-pneumatic(TN) LCD's), or significant portions of the substrate are not used, such as areas where wheels or clamps come into contact with the substrate.
Batch processing can overcome many of the disadvantages above regarding cleaning efficiency. For example, carrier racks or baskets can be constructed which contact the substrates primarily on the edges along the perimeter of the substrate rather than on the surfaces. In dip-tank processing, multiple immersion processes are used to treat, clean, rinse and dry the substrate. The carrier rack or basket is placed vertically into and from each process tank. The disadvantages of using this type of method are both the additional handling needed to load and unload the substrate from the carrier and also the relatively long length of time the basket or rack must be drained after each step to minimize dragout. Additionally, carriers or racks must be adjusted or re-fabricated for processing substrates of different sizes. Other batch processors sequentially perform several steps in one chamber, such as scrubbing, rinsing and drying, and as a result are relatively low in throughput. Overall, the batch-type processors typically perform with lower throughput than would be desired and/or require additional handling steps, both of which increase the cost of processing the substrates.
Therefore, there is a need for a relatively simple and cost effective method and apparatus for cleaning thin, sensitive substrates which has a high throughput rate which does not impart microscopic debris on the substrate surface and which allows minimum dragout.